1. Field of the Invention
The present invention relates to a degradable or compostable container for containing a liquid or liquid containing materials. The present invention further relates to a paperboard container having a degradable coating on at least one of the internal or external surfaces thereof. More particularly, the present invention relates to a paperboard container which will biodegrade to carbon dioxide, water and biomass under composting conditions. The present invention further relates to a method of making and a method of using the degradable container.
The present invention further relates to a degradable paperboard container which may be biodegraded initially under composting conditions and finally photodegraded as a humus or compost upon exposure to light.
2. Description of the Related Art
In the management of Municipal Solid Waste (MSW), the expectation that paper and paper products would biodegrade in landfills has proven to be unreliable. In fact, newspapers buried for over fifty years have been recovered from landfills in readable condition. Since paper comprises about 50% of landfill space, it has become an important priority to find alternate ways to manage paper waste.
Recycling paper, often with the removal of printing inks and coatings, has proven to be economically feasible when the recovered pulp fibers find new markets and applications. Fiber recovery and, in particular, repeated fiber recoveries tend to damage, break, and otherwise reduce the quality of paper fiber. This degradation in paper quality often results in a product with limited or nonexistent new markets or applications.
Since paper has the inherent property of biodegradability under appropriate conditions, more attractive alternates to simple landfilling have received increased attention. Among these is the process of composting, in which waste is degraded to humus or biomass under accelerated and controlled conditions of moisture, air, and microorganisms. More specifically, paper, under composting conditions is converted into carbon dioxide, water, and biomass (this process is also referred to as mineralization). The biomass is essentially comprised of microorganisms. Thus, the mass of waste is significantly reduced and the humus by-product has commercial value. Markets for the end-product of composting, usually referred to simply as compost or humus, are emerging. Compost, for example, is an excellent soil conditioner in marshy applications; and the uses of compost in wetland reclamation and water conservation appear quite promising. Compost is also used as a fertilizer and mulch in many farming and highway applications.
Paper products can be coated with resins or plastic materials to provide barrier properties when used in the containment of liquids. For example, U.S. Pat. No. 5,286,538 to Pearlstein et al., which is incorporated in its entirety herein by reference, relates to biodegradable and compostable containers for wet wipes comprising paperboard (about 85% by weight) with a polyethylene coating on both sides. In the composting process, microorganisms attack the cut edges of the container material leading ultimately to a biodegradation of the paperboard with a residue of polyethylene film.
Copending application Ser. No. 07/962,100 describes an improved product having a polymeric coating selected from among various aliphatic polyesters leading to a liquid packaging material ultimately capable of complete mineralization. However, the storage stability properties of aliphatic polyesters may not provide the optimum conditions for the storage of all products.
The need exists, therefore, to find suitable compositions and constructions for packages which are both compostable and effective barriers to moisture vapor. The most important requirements for these packages include:
a. barrier properties to reduce and prevent absorption and/or transmission of liquid components; PA0 b. heat sealability for carton construction and integrity; PA0 c. printability to provide attractive, non-functional graphics; PA0 d. vapor barriers to contain fragrances, flavors, moisture, etc.; PA0 e. barriers to oxygen and other ambient gases; PA0 f. rigidity, shape retention, and crush resistance, PA0 g. compostability to a humus with commercial value as a soil conditioner, where the humus is capable of ultimate mineralization.
The use of polyolefins and especially polyethylene in degradable liquid packaging has been described, for example, in U.S. Pat. No. 5,213,858 (Tanner et al.), which is incorporated in its entirety herein by reference. Tanner et al. relates to a coated paperboard having an inner coating of polyethylene and an outer coating of a biodegradable mixture of starch and polyethylene or a polyvinyl alcohol with some biodegradable properties. This combination of coatings, however, does not meet the above stated requirements. In particular, polyvinyl alcohol has an extremely high rate of moisture vapor transmission and its rate of biodegradation is slow. Further, starch filled resins have been shown to be only pitted by bacteria through selective attack on the carbohydrate. Furthermore, the inner coating is provided with no means at all for degradation.
Low density polyethylene is used extensively in liquid packaging. Among its most important attributes are low cost, heat sealability, barrier to moisture vapor, and clarity.
In fact, as described in copending application Ser. No. 07/962,100, particular blends of polyethylene and an aliphatic polyester such as polycaprolactone represent improvements in the moisture barrier properties of the polyester. Unfortunately, at levels significantly over about 30 wt % polyethylene, the rate of biodegradation is reduced to below practical levels.
Molded articles such as planters for seedlings made from aliphatic polyesters, as described in U.S. Pat. No. 3,867,324, when left in the ground are expected to ultimately biodegrade.
Specific blends of aliphatic polyesters and photodegradable polyethylene are described in U.S. Pat. No. 3,901,838 to Clendinning et al., for application in certain industrial and consumer plastic products which may degrade upon discarding. Similarly, U.S. Pat. No. 4,857,605 describes a blend of an aliphatic polyester with a photodegradable alternating copolymer of ethylene and carbon monoxide. The above three patents are incorporated in their entirety herein by reference.
As can be seen, a coated paperboard meeting the performance requirements of a liquid packaging material and capable of ultimate mineralization after composting has not been achieved previously.
Ever since their widespread use in packaging and related applications, plastics have been known to undergo a number of degradation processes which, in time, led to the undesirable loss of strength, embrittlement, discoloration, etc. These degradations are usually the result of changes in polymer molecular structure such as chain scission, unzipping of the polymer chain, and rearrangements leading to fragmentation and changes in cross-link density.
In the last forty to fifty years, major research efforts have led to successful solutions and preventive measures designed to avoid molecular breakdown, usually in the form of additives and selected polymer design. Greater understanding of the chemical and physical nature of degradation was invaluable in achieving these practical solutions. The mechanisms of hydrolysis, oxidation, and biological attack, often acting in concert, are known to be involved in most polymer degradation.
Looking ahead into the 21st century, the management of solid waste, particularly in the more densely populated regions of the planet, will become a matter of increasing concern. Solid waste from the packaging of food, personal, and medical products is certainly a major contributor to the overall problem. It has now become necessary to find ways to destroy the very materials that we have learned to stabilize and protect.
In the most preferred application of our knowledge and technology in this field, packaging materials would be designed to perform their intended function during manufacture, shipping, storage, and end-use; and then, upon disposal, would self initiate a degradation process leading ultimately to complete mineralization of the organic matter to water and carbon dioxide.
Now, in the present invention, it has been found that coatings of a biodegradable polymer on a first side of the paperboard and of a polyolefin such as polyethylene on the second side of a paperboard can be formulated and designed so that in the presence of composting conditions, degradation of the first coating and the paperboard substrate take place at an acceptable rate leaving the second side as a polyolefin residue. Furthermore, it has been found that when properly formulated, the polyolefin coating is photodegraded to carbon dioxide, water and biomass upon exposure to sunlight.